Protein Synthesis

Review for Keystone

Help! I broke a nail!

• What are nails made of?– A protein called keratin

• How does your body make a new nail to replace the one that broke off?– The body needs to make more keratin (Keratin is a protein. Remember: If it

ends in “in” it is a protein)

• In order to make anything what 2 things are necessary?– Instructions– Materials

In our bodies the making of new protein (like keratin) is called protein synthesis

•What serves as the instructions?DNA in the cell

•Where do you think the building materials come from?

from food! (protein that you eat is broken down into amino acids, the amino acids are then used to build the needed protein)

So HOW does it work?

• Your body makes proteins in 2 Parts:1. Reads, Copies, Edits the Instructions

(Transcription)2. Assembles the protein using amino acids and

following the transcript instructions (Translation)• To make new keratin to form a new fingernail

first you need the instructions• Somewhere in the DNA is one region that

provides the instructions for making keratin.What do you call a region of DNA like this that

“codes” for something?-a gene!

Part 1: TRANSCRIPTIONReading, Copying, Editing

the Gene• Where is this happening? Do you

remember where DNA is located?– In the nucleus, in the form of chromosomes

• Let’s pretend that this is the gene for keratin:

A closer look:

A T G T G G A G T C A C G G G T G A

T A C A C C T C A G T G C C C A C T

REMEMBER: The DNA code is made up of nucleotides, A, T, C and G A pairs with T C pairs with G

Only one side of the DNA strand is “read”. This side is called the template strand. Let’s say its this one

• Here is the tricky part. DNA cannot leave the nucleus. We need to make a complimentary copy of the gene and carry the copy out of the nucleus.

• An enzyme called _______________ locates the gene among all of the DNA, opens up the strand and produces a “transcript”, a complimentary strand of the DNA template

• The transcript is actually made of RNA. It is called an mRNA

RNA POLYMERASE

Now you make the transcript:

• Remember: The transcript is not an identical copy but a complimentary strand. If C is read, G is added to the growing transcript.

• Remember: Use U instead of T for RNA

• Your mRNA transcript should look like this:

Before this mRNA leaves the nucleus it is edited. Certain parts of the code are cut out.

The portions removed are called _____________. The portions that remain are called ____________.

A U G U G G A G U C A C G G G U G A

intronsexons

Lets say UGG and AGU are introns.What would the final mRNA look like?

TRANSCRIPTION IS OVER!All of this was happening in the nucleus. Now the final mRNA transcript leaves the nucleus and arrives at a ribosome in the cytoplasm for translation.

Final mRNA: A U G C A C G G G U G A

Part 2: TRANSLATIONReading the transcript and assembling the

correct amino acids into the protein needed

• Look at your final mRNA transcript. The code is read 3 nucleotides at a time. This is called a codon. Each codon corresponds to 1 amino acid.

• tRNAs carry over the correct amino acid and attach them together (form peptide bonds between them)

• How do you know which amino acids will come together to make the protein?

Use the genetic code!

The Genetic Code

What amino acids do you get for the codons in this

mRNA?AUG=CAC=GGG=UGA=

METHIONINE

HISTIDINE

GLYCINE

STOP

METHIONINE-HISTIDINE-GLYCINE = KERATIN (JUST AS AN EXAMPLE. The

actual protein is much longer)

REVIEW

TRANSLATION•Starts with the mRNA transcript•Happens at a ribosome•tRNAs do all the work•The final product is a strand of amino acids that fold into the protein!

TRANSCRIPTION•Starts with a gene for a particular protein•Happens in the nucleus•RNA polymerase does all the work•The final product is an mRNA transcript

What if the code is changed?

Any change in the DNA code is called a mutation.Sometimes the change still codes for the same amino acid and forms the same protein so there is no noticeable effect.Other times the change results in the wrong amino acid. The necessary protein will not form. This could result in a disorder of some kind.

From the pretest…

1. Which of the following is arranged from largest to smallest?

A. chromosome, nucleus, geneB. gene, nucleus, chromosomeC. nucleus, chromosome, geneD. chromosome, gene, nucleus

C. Nucleus, chromosome, gene

2. The pathway, DNA mRNA ribosome tRNA protein, taken by the genetic code during protein synthesis happens in

A.eukaryotes only.B.all organisms.C.prokaryotes only.D.no organisms.

B. ALL organisms (prokaryotes do not have a nucleus but they have ribosomes)

THIS IS THE CENTRAL

DOGMA OF BIOLOGY!

(CORE CONCEPT)

3. Structure 1 aids in the process of protein synthesis by

A. providing the code for assembling a protein.B. assembling a protein.C. providing the energy needed for protein

synthesis.D.allowing the movement of substances into the

cell for the process of protein synthesis.

B. Assembling a protein.

This is a ribosome

Use the chart to help you answer number 25.

Codon Amino Acid Codon Amino Acid UUU Phenylalanine AUC Isoleucine UCA Serine GUC Valine CAA Glutamine AAU Asparagine GCG Alanine GAC Aspartic acid CAG Histidine CCG Proline AUA Isoleucine CUA Leucine

1. Diabetes is a disease characterized by the inability to break down sugars. Of ten

a person with diabetes has a defective DNA sequence that codes f or the making

of insulin protein. Suppose a person has a mutation in his/ her DNA and the fi rst

triplet f or the insulin gene reads T A T instead of T A G which is the normal

gene f or insulin. Will the person with this mutation be diabetic?

A. Yes, because any mutation will cause disease.

B. Yes, because the insulin protein will be changed.

C. No, because the insulin protein is still produced.

D. No, because it is a gene mutation and not a chromosomal mutation.

C. AUA and AUC both code for the same amino acid, isoleucine